A wide range of vehicles and methods are known for transporting human subjects. Typically, such vehicles rely upon static stability and are designed for stability under all foreseen conditions of placement of their ground-contacting members with an underlying surface. For example, a gravity vector acting on the center of gravity of an automobile passes between the points of ground contact of the automobile's wheels and the suspension of the automobile keeps all wheels on the ground at all times making the automobile stable. Although, there are conditions (e.g., increase or decrease in speed, sharp turns and steep slopes) which cause otherwise stable vehicles to become unstable.
A dynamically stabilized vehicle, also known as a balancing vehicle, is a type of vehicle that has a control system that actively maintains the stability of the vehicle while the vehicle is operating. In a vehicle that has only two laterally-disposed wheels, for example, the control system maintains the fore-aft stability of the vehicle by continuously sensing the orientation of the vehicle, determining the corrective action necessary to maintain stability, and commanding the wheel motors to make the corrective action. If the vehicle losses the ability to maintain stability, such as through the failure of a component or a lack of sufficient power, the human subject can experience a sudden loss of balance.
For vehicles that maintain a stable footprint, coupling between steering control and control of the forward motion of the vehicles is less of a concern. Under typical road conditions, stability is maintained by virtue of the wheels being in contact with the ground throughout the course of a turn. In a balancing vehicle with two laterally disposed wheels, however, any torque applied to one or more wheels affects the stability of the vehicle.